Extended signaling system and method

ABSTRACT

Embodiments are described that include a “front end” device located remotely from a local telephone location. The front end filters DC and AC current on a telephone line to separate these signals and passes a DC current through a low resistance Low Pass Filter without traditional resistance or current limiting means. The front end also provides signaling capability isolated from the DC and audio channels by a High Pass Filter. Some embodiments also include a “back end” unit located near a local telephone location. The “back end” unit filters the DC and AC currents into at least two DC current streams. One of the DC current streams provides sufficient current to power a local telephone. The other stream(s) provides current sufficient to power an auxiliary device. The “back end” device may also provide signaling isolated from the DC and audio channels that is complementary to the “front end” signaling.

I. RELATED APPLICATION

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/191,083 entitled “EXTENDED SIGNALING SYSTEM ANDMETHOD” filed on Sep. 5, 2008, which is hereby incorporated by referencein its entirety.

II. FIELD OF THE INVENTION

The present invention relates to a device and method to enable a finiteelectrical power source to deliver more power to the point of use over adefined transmission channel and provide additional signaling capabilitybetween the termination points of the defined transmission channel

III. BACKGROUND OF THE INVENTION

Traditionally, “plain old telephone service” or “POTS” has beenfacilitated using a low voltage, low current combination of DC and ACsignals transmitted over the telephone network to a local telephone.This has been sufficient to power the functionality of a simpletelephone and to generate, transmit, and receive modulated AC signalsfor voice transmission. The electrical current necessary to enableoperation of a local telephone is typically about 25 milliamps.

Modern telephones have an expanded array of features such as visualdisplays, speakerphones, recording/messaging, portable handset and othercapabilities. The power necessary to enable these capabilities exceedswhat is available from the telephone network at a local telephone.Simply stated, telephone network current is not sufficient to poweranything but the telephone itself. As a result, one or more additionalexternal power supply units are required to furnish the necessarycapability. Frequently, these power supply units take the form of AC/DCadaptors that are plugged into a standard 110 AC wall socket and theoutput of which is connected to the telephone or peripheral devices.These so-called “wall-warts” provide the additional power required tosupport the added functions/capabilities and devices (e.g., batteryoperated wireless handset) associated with the telephone.

Likewise if electronic “data” services, such as ISDN or DSL, are to betransported on the same pair of conductors to, or near to, the localtelephone instrument, yet another “wall-wart” is almost certainlyrequired to power the associated modem device. For convenience thesetelephone instruments and modem power sources are referred to as being“AC line powered.”

While wall-warts are unsightly and cumbersome they are acceptable formost purposes to provide the additional power (i.e., power beyond whatis supplied by the CO/CB/SLC/IAD/PBX over the telephone network) to ACline powered devices.

Nevertheless, there are situations where some telephone-relatedcapability or feature is desired that requires additional power but islocated in an environment where AC line power is not available. This canbe the case wherever wiring was put in place specifically for telephoneapplications. Existing incarceration facilities, particularly olderprisons and jails, are one example of such an environment. Theseinstitutions typically provide POTS telephone services as an amenity forthe inmates to conduct necessary and/or interpersonal communicationswith those on the “outside.” Recently, such institutions have desired tosupplement POTS service with additional capabilities. For example, it ishighly desirable to increase the accuracy of inmate identificationrequired to access outside phone service by using fingerprint, barcode,RFID, or other types of readers that can identify or verify the inmateby thumb print, palm print, voice print, retinal scan, or anotheridiosyncratic physical characteristic, or information embedded within awristband. It is also desirable to enable a telephone with visualtwo-way camera and picture capability so that the phone can be used as avehicle for remote visitation from a site near to or far from that ofincarceration to avoid excess prisoner movement.

Penal institutions are also finding it increasingly desirable to providelimited Internet or more commonly a restricted service Intranet accessto inmates for purposes of accessing an inmate account, conductingtransactions, etc., all of which require a modem or similar device toconnect to the Intranet via the telephone network. All of theseperipheral devices require additional power. A typical peripheral devicemay require about 60-70 milliamps at some low voltage such as 3-12 VDC.When one or more of these peripheral devices are desired, powerrequirements may exceed more than 125 milliamps. The equivalent powerrequired for these devices is far in excess of the 25 milliampsavailable and intended to operate the telephone itself. The DC currentavailable from the telephone network typically barely exceeds the 18-20milliamp minimum requirement recommended for reasonable conversationquality.

Due to the understandably unique requirements of such facilities,certain infrastructure features available in other buildings, e.g.,crawl spaces, hollow walls, AC outlets, are simply not permittedadjacent to or near the physical locations where a telephone ortelephone and data device may be desired or needed. Absent the accessthat may be available in a more typical structure the cost of rewiringfor example from a 25-pair cable distributed to many cell blocks andindividual station locations to separate CAT-5 cables is simply costprohibitive, often by orders of magnitude. Likewise the cost to providenew AC power near to the required location, and provide that powersource with appropriate physical security for both the outlets, the‘wall-warts’, and the low voltage from the warts to the actualinstruments is usually little short of astronomic. And neither option,even if financially possible, could be accomplished in a time framesimilar to that required in a commercial building situation due to thesecurity, controlled access, and physical detritus and debris related tosuch an undertaking.

Nevertheless, there are emerging pressures (e.g., service delivery,social pressure, cost containment, and manpower reduction reasons) toprovide newer telephony related and additional service deliveryinstruments to these same facilities and difficult locations.

In the absence of available AC power, there are two possible solutions.First, replace the existing POTS, or POTS-like wire pair with either alarger gauge wire or greater number of conductors to each telephone toreduce the resistance to current and facilitate the delivery of greaterpower to the telephone location. For example, a single UTP could bereplaced with a full CATS quad pair cable. In many inmate or similarfacilities, this is not realistic or perhaps even possible for many ofthe same reasons that it is not possible to supply AC power.

More recently, it has been proposed to “bleed” a small amount of excesscurrent not required for powering the telephone to charge one or morelocal batteries that would then be used to provide power to the device(e.g. fingerprint reader) supplying the supplemental capability orfeature. This implementation has the disadvantage of requiring a‘recharge’ time period between instances of device use and cannot berelied upon to provide adequate power in situations of high-use orunexpected use patterns. Using a fingerprint reader as an example, thetaking of a fingerprint reading and transmitting that informationthrough the network for verification would result in at least somedischarge of the battery while powering the fingerprint reader. Sincethe fingerprint reader is likely to require much more power than isavailable from the telephone line to charge the battery, the state ofthe battery charge will be diminished and will eventually, throughconstant use, be unable to provide adequate power to operate thefingerprint reader. The device user must now wait some period of timeuntil the battery has time to recharge to a usable threshold before theuser can continue his use of the device. A simple misdial of thetelephone number and subsequent redial by the user could possibly causeenough discharge of the supply battery to fail the redial attempt whichis deemed to be unacceptable operation for most applications.

The use of various example identification enhancement devices mentionedabove entails a variety of, typically low speed, controls andcommunications protocols to, for example, enable and disable a device,provide operational instructions to the device user, and thecommunication of results or other output from the device to a decisionmaking point such as a centralized control system.

In the current implementations of many of these devices they are alwayspowered whether needed or not, instructions to the user are oftenprovided by playback of a verbal recording from a centralized controlsystem, and the device results are transmitted via DTMF or other audiblesignaling means. The local telephone instrument is commonly utilized toprovide the user instructions which tends to extend the call setup timebut in any case prevents the use of the local telephone for its primarypurpose when being used to provide instructions. Likewise when theexternal device such as a biometric characteristic reader is reportingits findings by the use of DTMF tones additional time is required withinthe overall call setup process. It is no longer an over-zealous conceptto deactivate power using devices when not actively performing afunction but most current biometric devices will, at best, move to someform of lower power state when not actively performing their respectivebiometric functions but generally have no means to deactivate when notrequired for a particular, or over an extended, period of time. The useof DTMF signaling to communicate results can have the additionaldisadvantage of providing audible clues to inmates in a penalinstitution situation or for third parties to record otherwise secureinformation. In either case the information can later be mimicked orused for unintended purposes.

Accordingly, a need exists to supply additional power over the existingdelivery system infrastructure to provide greater power at the localtelephone location to enable both the normal operation of the telephoneand additional capabilities, features or devices. Likewise a need existsto provide some level of control and signaling over that same deliverysystem that does not use the bandwidth originally provided for telephoneconversations. It is with respect to these and other considerations thatembodiments of the present invention have been made. Although relativelyspecific problems have been discussed, it should be understood thatembodiments of the present invention should not be limited to solvingthe specific problems identified in the background.

IV. SUMMARY OF THE INVENTION

The deficiencies of the prior art are solved using the method and systemof the present invention. In embodiments, the invention enables a finitesource of DC and AC current typically provided to enable use of atelephone to deliver more current through a previously definedtransmission channel between the source and the local telephone and alsoprovides a mechanism to exchange telephony and non-telephony relatedsignals, in the form of states or data, between a distribution locationand equipment associated with the local telephone or telephony relatedinstrument. While the typical −48VDC powered telephone line is onlysufficient to provide about 25 milliamps of DC current to a localtelephone instrument over its existing infrastructure, the invention inembodiments permits that same −48VDC level to deliver a current inexcess of 25 milliamps to the same telephone or instrument location overthe same existing wiring and infrastructure while adding additionalsignaling capabilities. This is accomplished by employing a “front end”device typically located at a point in the transmission channel remotefrom the local telephone such as at the service entrance of the networkinto the building or at an appropriate distribution frame. The front endperforms several functions including filtering the DC and AC current onthe transmission channel to separate these signals and passing the DCcurrent through a low ESR (equivalent series resistance) LPF (Low PassFilter) without traditional additional resistance or current limitingmeans and resettable fuses to prevent damage to the source of DC and ACcurrent in the event of a short circuit or other overload condition.Typically, the fuses replace one or more series resistances or otherdevices that are generally employed to protect the network fromelectrical short conditions, but have the disadvantage of addingsignificant resistance to the flow of electrical current. The front endalso provides an audio (speech frequency range) channel for telephonycommunications use isolated from the DC path by a BPF (Band Pass Filter)as well as a high frequency (out of band) signaling capability isolatedfrom the DC and audio channels by a HPF (High Pass Filter). The systemalso employs a “back end” unit located at a point on the transmissionchannel at or near the local telephone location. The “back end” unitsplits the DC and AC currents into at least two DC current streams. Oneof those streams provides sufficient current to power the localtelephone. The other stream(s) provides current sufficient to poweradditional capabilities, features or devices associated with the localtelephone, such as a biometric reader. The back end unit also splits theAC signals into an audio channel, via a LPF, for telephony conversationpurposes as well as to an out-of-band signaling channel, via a HPF, forstate and/or data signaling purposes. By use of this methodology andsystem, the same power source can deliver 40-60 milliamps or more to thelocal telephone and associated peripheral devices instead of the usual25 milliamp current. By the application of a power conversion subsystemthe extra current not utilized by the local telephone is converted to alower voltage but yet higher current which is made available to externaldevices such as the example biometric reader. For example, the systemcan provide 100 milliamps or more at 5 volts to such an external deviceassociated with a local telephone or similar use device over 4000 feetof standard 24 AWG UTP in addition to one or more out-of-band signalingchannels and still provide normal telephone communication capabilities.

This summary is not intended to identify key features or essentialfeatures of the claimed subject matter and should not be used to narrowthe scope of the claimed subject matter. This summary is provided onlyto generally provide a description of some of the embodiments of thepresent invention.

V. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing a typical POTS system for delivering “landline” service to a local telephone. It is labeled as “prior art” becauseit existed prior to the present invention.

FIG. 2 is an overall schematic of an embodiment of the present inventionshowing how the major functional blocks are interconnected to providethe electrical, audio, and signaling terminations.

FIG. 3 is a circuit schematic showing in more detail an exampleimplementation of one embodiment of the Head-End of the presentinvention.

FIG. 4 is a circuit schematic showing in more detail an exampleimplementation of one embodiment of the Tail-End of the presentinvention.

FIG. 5 is a flow diagram depicting one embodiment of the signalingoperations as may be implemented at the Head-End of the presentinvention.

FIG. 6 is a flow diagram depicting one embodiment of the signalingoperations as may be implemented at the Tail-End of the presentinvention.

VI. DETAILED DESCRIPTION OF THE INVENTION

The principles of the present invention may be further understood byreference to the following detailed description and the embodimentsdepicted in the accompanying drawings. Note that like items in multiplefigures have like item numbers.

FIG. 1 is a simplified depiction of a traditional “plain old telephonesystem” (“POTS”) telephone subscriber circuit including pertinentelements at a Central Office (“CO”), the “outside plant,” and at thelocation of the end customer instrument, i.e., “local telephone” and anyperipheral functions or devices. It is provided as context in that itrepresents: (a) how telephone current is provided to the local telephonein the absence of the present invention and (b) the electricalrelationship of major on-premises components. FIG. 2 is a depiction ofan embodiment of the invention which: (a) provides electrical, audio,and signaling termination for the subscriber location as seen by thetraditional POTS network and (b) shows the arrangement of circuitelements which provide the additional power and functionality which willbe then conveyed to the terminating equipment end of the completesystem.

FIG. 1 depicts a very high level view of a subscriber telephoneinstrument 20, the “Serving Wire Center” 1 (“SWC”) for a specificcustomer, the subscriber premises 12 where the telephone instrument 20is located, the telephone line 11 connecting the two locations, and thecustomer premises inside wiring telephone line 17 that provides all butthe final few inches or few feet of connectivity to telephone instrument20. The serving wire center 1 is very commonly referred to as the“Central Office” (“CO”) even though the specific equipment that pertainsto the specific subscriber may actually be located at some pointphysically closer to the subscriber for example within a “RemoteTerminal” (“RT”), a “Subscriber Loop Carrier” (“SLC”) installation, orfrom a “Channel Bank” (“CB”) which may be located within the subscribersor a nearby building or in a “Controlled Environment Vault” (“CEV”) nearthe subscribers location. In most cases regarding the above examples,the equipment and functions mentioned may belong to the Local ExchangeCarrier (“LEC”). For purposes of the present invention, thefunctionality of the SWC may also be provided by any other moderncommunications mechanism including, for example, an “Integrated AccessDevice” (“IAD”), a “residential gateway” (“RGW”), a “Private BranchExchange” (“PBX”), an “Inmate Communications Control System” (“ICCS”),or any other system appropriate to the purpose as may be recognized byone skilled in communication arts. Further, such equipment may well notbe owned or operated by the LEC but rather may belong to an entityassociated with the physical premises or some unrelated third party. Inthat context, the following is a brief description of POTS features anditems that provide context for the present invention.

The SWC requires a power source to run everything within its ownconfines but traditionally also provides the subscriber loop biascurrent to each customer such that the subscriber no longer has toprovide their own individual battery system, as was the case prior tothis practice being adopted as a standard practice. This core powersource 2 comprises major elements such as AC mains powered batterychargers, optionally a backup generator in case of AC mainsinterruption, storage battery systems that provides uninterrupted powerto operationally critical systems, including the loop bias current tothe subscribers, and the “ring generators” (“RG”).

The SWC may be thought of as having two very basic types of equipment toprovide normal operations. The common equipment and systems 3 includeall shared and non-subscriber specific equipment and functionality. Thesubscriber dedicated equipment including the “Subscriber Line InterfaceCircuit” (“SLIC”) 4, current and voltage limiting, fusing protection,surge and lightening protection equipment 9, and the final subscriber“Tip and Ring” terminals 10, including the equipment, wiring, andfunctionality that is duplicated for and dedicated to individualsubscribers. The various forms of equipment power for the commonequipment is indicated by signal 5, while the battery and ringingvoltages provided to each subscribers SLIC are indicated by signal 6.Those skilled in the art will recognize that among the functions withinthe SLIC subsystem is, as mentioned above, the limiting of the loopcurrent to the subscriber terminals 10. Most often the SLIC isconfigured such that the current drawn from the SLIC will not exceedapproximately 100 milliamperes (mA) if the subscriber pair is directlyshorted together. Those skilled in the art will recognize that,primarily due to line resistance between terminals 10 and terminals 13,the actual off-hook loop current will normally be substantially lessthat the 100 mA limit and that the “Outside Plant” (“OP”) is normallyengineered to provide at least 18 mA loop current on the longest lines.Experience has shown that the most common range of off-hook loopcurrents is 22 mA to 35 mA. Signal 8 refers to the two-wire, typically“unshielded twisted pair” (“UTP”), associated with the physical wirescarrying bias current, ringing voltage, signaling, and bi-directionalvoice frequencies between the SWC and the subscriber. Signal 7 refers toa set of physical and electrical signals which are often insignificantly different formats as compared to those appearing on signal8. Signal 7 includes many uni-directional signals to convey voicefrequency signals, and control signals as are appropriate for theimplementation of the SWC in question.

Signal 11 is simply a representation of all of the OP wiring andpossible equipment used to implement the transportation of the signalsavailable at the SWC terminals 10 to the subscriber location 12. Thetelephone service provider is normally responsible for appropriateprotection to the subscribers internal wiring from the anticipatedeffects of lightning, high voltage transmission line induced voltages,accidental connection of undesired voltages, etc., from the OP wiring11. Protection is indicated in the SWC by protection equipment 9connected between the subscriber side “Tip and Ring” terminals 10 andthe SWCs internal “Tip and Ring” signals 8, and indicated in thesubscriber location elements 12 by protection equipment 14 connectedbetween the SWC side “Tip and Ring” terminals 13 and the subscriberson-premises “Tip and Ring” signals 15.

The subscriber connection 19 to the local telephone instrument 20 may bethe only apparent connection, as far as the subscriber is concerned,between the telephone service provider system and the telephoneinstrument 20. Those skilled in the art are aware that within theborders of the subscriber location 12 there exists a few physicalelements that are normally transparent to the users of the telephoneinstrument 20. Elements pertinent to the present invention include thefunctional point of demarcation 16 (“DEMARC”) between the LEC andcustomer premises equipment (“CPE”) including perhaps a firstdistribution frame often referred to as the Main Distribution Frame(“MDF”) which would be in near proximity to the DEMARC, inside wiring 17(“IW”), which may include one or more additional intermediatedistribution frames (“IDF”), leading eventually to some sort of jack,punch-down block, or other termination connection point indicated aspoint 18 in the figure, and finally, the connection 19 to the telephoneinstrument 20 itself. For reference purposes, those skilled in the artrecognize that a conventional telephone instrument 20 embodies bothaudio or conversation, transceiver functionality, and also certain AC(alternating current) related capabilities such as customer alerting,Ringing, and certain DC (direct current) related functionalities ofwhich the existence of loop current, or the on-hook or off-hook statusof the telephone instrument, and the range of values of the amount ofcurrent when the instrument is in its off-hook state is relevant to thepresent invention. Those skilled in the art will understand that theforegoing is only a brief description of selected elements of atraditional telephone circuit and is not intended to be comprehensive,but rather to provide reference points for the description of theembodiments of the present invention that follows.

FIG. 2 provides a depiction of an arrangement of elements that describesan embodiment of the present invention.

FIG. 2 includes a depiction of an arrangement of elements that operatingtogether may be referred to as the “Head End” (“HE”) or “front end”functionality in one embodiment of the present invention. Subscriber Tipand Ring signal 15′ is the same signal as its corresponding signal inFIG. 1. As previously stated, it is an object of the present inventionto provide additional power and functionality and to make thisadditional power and functionality available at the local telephonelocation. This improved power can be delivered even if a traditionaltelephone instrument is not actually employed at that location or if thetelephone is not employed for the traditional purpose of voice“telephone” communications. In other words, the increased power can beused to enable some communications device or one or more otherinstrument or capabilities employed with, or in lieu of, the localtelephone. Communications devices examples include telephones, speakerphones, non-telephone, yet telephone-like instruments, such as a videophone or non-telephone-like devices that may optionally includetelephone communications features such as a computer or microcontrollerbased display and user interface device primarily intended to accessdata or inmate related services. Some of these communications devicesmay traditionally be AC line powered devices.

FIG. 2 also includes a depiction of an arrangement of elements thatoperating together may be referred to as the “Tail End” (“TE”) or “backend” functionality in one embodiment of the present invention. Localtelephone instrument Tip and Ring signals 19′ and the local telephoneinstrument 20′ are the same elements and signals as their correspondingelements and signals in FIG. 1.

FIG. 2 also includes elements 16′, 17′, and 18′ which are the same IWfunctionalities as those presented in FIG. 1.

It may now be recognized that FIG. 2 HE elements 21 thru 43 are, in anembodiment of the present invention, interposed between signal 15 andterminal 16 of FIG. 1 as indicated by their like elements 15′ and 16′ inFIG. 2. Likewise, it may now be recognized that the FIG. 2 TE elements70 thru 90 are, in an embodiment of the present invention, interposedbetween terminal 18 and signal 19 of FIG. 1 as indicated by their likeelements 18′ and 19′ in FIG. 2. As indicated in FIG. 2, telephoneinstrument 20′ does not have an unimpeded sequence of direct electricalcontinuity between signals 15′ and 19′.

Those skilled in the art may now follow the signals and mechanismsprovided by the present invention as depicted in the embodimentpresented in FIG. 2.

In an embodiment of the present invention, FIG. 2 indicates that atelephone instrument 20′ is located at its original or local locationand uses some “last inch” cable to provide connectivity of signal 19′ towhat it perceives as a SLIC or “Foreign Exchange Station” (“FXS”)signal. This signal, in terms of DC voltage range, bias current, on-hookand off-hook control signaling, and optional alerting or ringing signalsare functionally provided by a plurality of mechanisms now to bedescribed.

In FIG. 1, the bias current, or “Talk Battery”, is provided to telephone20 from the distant source 2 without regard to the actual equipment,capabilities, purpose, or location of SWC, or alternative entity 1,keeping in mind that this bias current is typically around 25 milliampsat telephone 20. Likewise, the alerting or ringing voltage for telephone20 is provided from the distant source 2, while the on-hook or off-hookstatus of telephone 20 is detected, from the SWCs point of view, bydistant element 4. In FIG. 2 it can be appreciated by those skilled inthe art that the SWC provided bias current may not be directlycommunicated through the elements depicted all the way to telephone 20.Those skilled in the art will also appreciate that SWC generatedalerting, or ringing voltages, may not be directly communicated throughthe elements depicted all the way to telephone 20. Likewise, one skilledin the art would appreciate that the on-hook or off-hook status of 20may not be directly communicated through the elements depicted all theway back to the SWC loop current detector. A more detailed examinationof FIG. 2 will explain how the previously mentioned current and signalequivalents may be provided.

In the embodiment shown in FIG. 2, bias and signaling voltages andcurrents are communicated via signal 15′ between the SWC function andthe “Foreign Exchange Office” (“FXO”) port 21 of the HE portion. Thesevoltages and currents are then communicated by signal 22 to relayfunction 23 whose operation will be seen by one skilled in the art asbeing analogous to the hookswitch function in a traditional telephoneinstrument. However, a major difference between the traditionaloperation and that of the embodiment shown in FIG. 2 is that in theembodiment, the subscriber does not have physical or direct control ofthe hook switch function provided by relay function 23.

Relay function 23 is depicted in its on-hook state and thus voltagesappearing on signal 15′ will be communicated via relay function 23 andsignals 22 and 25 to Ring Detector 24. Signal 26 is representative ofthe current ringing state of signal 15′ and communicates this stateinformation to Signal Transceiver and Controller 27 (“STC”). An alertingsignal from the SWC functionality will thus be detected by Ring Detector24 and forwarded via signal 26 to STC 27. Assume for the purposes ofthis description that this embodiment of the present invention isexpected to forward the SWC alerting state to the local telephone 20′.This may not be the case in another embodiment such as in an embodimentintended for use with an inmate telephone control system where incomingcalls would normally not be expected, nor would such calls normally beextended towards an inmate accessible telephone instrument. In theexample embodiment, signal 26 does not directly cause an audible,visual, or other conventional ringing indication.

The STC may, depending upon the needs of a particular embodiment, encodea new signal 42 onto a higher frequency carrier where this carrierfrequency is greater than the traditional telephony sampling frequencyof 8,000 samples per second. Preferably, the carrier may be somemultiple of 4 KHz. Those skilled in communications art will understandthat should some of the energy of this carrier frequency reach the SWCvoice frequency digital encoding device, e.g. a CODEC, then that energy,due to the effective under-sampling per Nyquist's theory, would resultin an aliased or phantom frequency energy within the 0 to 4 KHz voicefrequency range. This potential effect is minimized when the carrierfrequency is a multiple of 4 KHz as the resulting aliased signal will benear zero Hz and thus be inaudible to persons on the related telephonecall. To further attenuate any potential unwanted energy from the STCwithin the voice frequency communication frequencies, a “High PassFilter” 43 (“HPF”) may be provided. This is not intended to limit thecarrier frequency to some multiple of 4 KHz, as HPF 43 may be configuredto provide adequate isolation between the voice frequency range and thedesired carrier frequency. For example, an HPF 43 required to adequatelyattenuate carrier frequency energy above 20 KHz may be implemented.Alternatively, it may be convenient to use two or more carrierfrequencies where each carrier frequency is also a multiple of 4 KHz, ormay have no special relationship to 4 KHz, so long as HPF 43 providesadequate isolation between the voice frequency range and the selectedcarrier frequencies. Moreover it may be convenient to use one or morecarrier frequencies in each direction, i.e., one or more carrierfrequencies from HE to TE (as described later), and the same or adifferent one or more carrier frequencies from TE to HE. The output ofHPF 43 is coupled to a common bus 35 that provides for the combining ofsignals, which will be described below, onto a single wire pair so as toprovide novel capabilities.

While the following will be more completely described, please assumethat an appropriate off-hook representation signal, again encoded ontothe high frequency carrier previously described, or encoded onto yetanother useful carrier frequency arrangement, is sent from the TE systemdepicted in FIG. 2 and thus appears on the common signal bus 35 of FIG.2. When the encoded signal presently being considered passes through HPF43, it will appear to STC 27 on signal 42, which is a bidirectionalsignal, where STC 27 may receive the signal, decode the command, and inresponse to the command, send signal 29 to relay coil 28 causing relaycontacts 23 to connect signal 15′ to signal 32 and thus to couplerelement 31.

Coupler 31 provides three principal functions: first, to provide DC looptermination toward the SWC; second, to couple traditional voicefrequency energy in the range of approximately 300 Hz to 3500 Hzbi-directionally between signals 32 and 33; and third, to provide DCisolation between signals 32 and 33. This coupler may be either passive,if some small insertion loss is acceptable, or active if there is arequirement to compensate for, and thus minimize any voice frequencyartifacts. Another function of coupler 31 is to, under abnormalconditions, attenuate the relatively high ringing voltages from passingthrough to signal 33 which is primarily intended to be limited totraditional voice frequency energy. Normally relay 23, 28 preventsringing voltage from reaching coupler 31. To further ensure this isaccomplished, a “Band Pass Filter” (“BPF”) 34 may be provided prior tocoupling signal 33 to the common signal bus 35.

As mentioned previously, coupler 31 provides DC loop current terminationtowards the SWC. Those skilled in the art will recognize that with thisarrangement there is no bias power available to power either the HE STC27 or the telephone instrument 20′ that the subscriber would presumablyuse. Therefore, the embodiment of the present invention shown in FIG. 2provides a novel arrangement to satisfy those needs, but also to providenew and additional capabilities that will become evident. A master powerelement 36, as depicted in FIG. 2, may be an AC line powered supply, abattery, perhaps some other DC power source, or a combination of theseconfigured to supply a DC voltage to power signal 37 to an effectsomewhat similar to the SWC battery function.

Those skilled in the art will understand that the power signal 37appears very much like a large capacitor which would effectively shortout or highly attenuate virtually any AC signals such as voice frequencyor higher frequency signals, if those signals were to be connecteddirectly to power signal 37. Those skilled in the art will recognizethat the BORSCHT functions, and particularly the battery feed to thehybrid of a SWC SLIC function, is intended to prevent this non-DCshorting effect. In the embodiment shown in FIG. 2, the traditionalBORSCHT functions are foregone and only a “Low Pass Filter” 38 (“LPF”)is used to prevent non-DC signal attenuation and to provide anon-current limited DC bias to the signal passed from LPF 38 to commonsignal bus 35 to novel effect. Elements 36 and 38 together are providedto present a relatively low “equivalent series resistance” (“ESR”)towards the signal passed from LPF 38 to common signal bus 35 at DC anda high ESR generally for AC signals including AC signals at voicefrequencies and above. Although this arrangement may hint at thoseadvantages later to be described, it also presents some potentialproblems. If signal 35 were to be directly connected to HE outputterminals 16′ and if the terminals 16′ were shorted, there would existthe same sort of over currents that would exist if a SWC did not providecurrent limiting to its own subscriber circuits

The protection fuses in traditional protection element 9 in FIG. 1 arechosen to protect against major faults such as inadvertent connectionsto AC mains (110/220, etc.) but are not intended to specifically limitthe SWC loop current to 100 milliamps as that is accomplished by thebattery feed resistors of the SLIC. In embodiments of the presentinvention, a useful current limit may be provided with “precise” fusesor a current foldback circuit. Protection element 39 in FIG. 2 may alsoprovide lightning protection similar to that provided by element 9 inFIG. 1.

FIG. 2 also depicts an arrangement of elements that operate together toform what may be referred to as the “Tail End” (“TE”) or “back end”functionality of the present invention. IW telephone line 17′ in thefigure carries the higher DC current capability presented by the HE aspreviously described as well as voice frequency energies and the higherfrequency carrier encoded bi-directional signals as previouslydiscussed. The signals on IW telephone line 17′, which may be considereda modified form of Tip and Ring signals, appear on the TE terminals 18′and may be connected to protection element 71. Protection element 71would conveniently have many characteristics similar to those ofprotection element 39 including a low ESR throughout its design currentrange as well as lightning and induced voltage protection and excessivecurrent limiting as its function would be most beneficial if IWtelephone line 17′ were either relatively long, perhaps thousands offeet, or if it traversed open distances between buildings wherelightning or power lines may induce undesirable voltage or currents intoit, or both. One skilled in the art will recognize that in many casesprotection elements 71 or 39, or both, would not be necessary in aparticular embodiment. For example, if power source 36 implementationincludes the current foldback characteristic previously mentioned, thenfuse elements 49, 50 of FIG. 3 are not required for short circuitprotection purposes which would result in the overall ESR of the HEbeing reduced by the ESR due to these fuses. With this in mind, it maybe seen that the DC voltage, voice and carrier frequency energies on IWtelephone line 17′ are coupled to common signal bus 72 which isfunctionally somewhat similar to common signal bus 35. The embodimentshown in FIG. 2 also contains element 73 which is a LPF withcharacteristics substantially similar to those of LPF 38. LPF 73 thencouples primarily only the DC portion of the signal on common signal bus72 to the input sides of local power source 75. Note that power source75 may conveniently be implemented as one or more “switch mode powersupplies” (“SMPS”) depending upon the needs of the specificimplementation. Power source 75 is provided to supply any local biaspower such as to STC 77 and to provide some limited amount of power toan external device or system such that that external device or systemdoes not require a local, generally AC mains derived, power source. If aspecific implementation requires different voltages either for functionsinternal to the TE or for the TE circuitry and for an optional auxiliarydevice, then local power source 75 may be composed either of appropriateindividual power conversion elements or a single conversion system withmultiple outputs as would be appropriate for the implementation. In anycase, it is appropriate to configure the local power source such that anoverload condition presented to the auxiliary power signal 88 could beappropriately managed and yet would not interfere with any other TEoperational capability.

Element 78 in FIG. 2 is a LPF whose upper frequency characteristicswould normally match the similar characteristics of BPF 34. Element 78is a LPF so that the DC component of the signal on common signal bus 72may be utilized to provide bias current to a telephone instrument suchas 20′ should such be connected to telephony output terminals 87. Sincethe power source for the signal on common signal bus 72 derives from thelow resistance source 36, 37 a local current limiting means is providedby a Constant Current Limiter (“CCL”), an element of 80. Per previouslynoted experience, the CCL may conveniently be configured to provide, forexample, 22 to 30 mA to a telephone instrument 20′ when in its off-hookconfiguration. Thus signal 79 contains: (1) DC voltage with its currentlimited only by the resistance of LPF 38, telephone line 17′ andresistances within, and protection limits of optional elements 39 and71; (2) the voice frequency energy path needed for telephone 20′ whilethe CCL controls that loop current at signal 86 to its preconfiguredvalue.

An Off-Hook Detector, an element of 80, is provided to sense when atelephone instrument 20′ is in its off-hook configuration. The status ofthe on-hook or off-hook configuration is reflected by the state ofsignal 88 being presented to STC 77. STC 77 would encode this onto asignal sent towards the HE STC 27 in a manner similar to that describedearlier for the ring detection signal being encoded and sent from STC 27towards STC 77. Likewise, when STC 77 receives a signal from STC 27interpreted as ringing from the SWC, STC 77 would activate signal 85 toenable an optional local ringer 84. Optionally, ringer control signal 83may enable Ring Generator (“RG”), an element of 80, which may activate aconventional ringer device in telephone 20′, should one exist. If an RGis not provided in a particular implementation, then the ACcharacteristics of signal 86 are the same as those of signal 79, elsesignal 86 has the additional capability of including the ringing voltageprovided by the RG. Signal 86 is the TE local telephony signal, voltage,and current set presented to output terminals 87.

In a similar manner the off-hook encoded signal sent from STC 77 to STC27 may now be recognized by STC 27 which would utilize signal 29 toactivate relay coil 28 to energize relay contacts 23 to effectivelyconnect coupler 31 towards the SWC or appropriate SWC-like equipment asan off-hook event.

It is now apparent that the above descriptions explain how theembodiment of the present invention shown in FIG. 2 may advantageouslyuse the low ESR characteristic of the HE to provide an auxiliary powersource at the TE location. First, the HE device may providesignificantly more power to its output terminals 16′ principally due tothe low ESR of the HE design. Further, a telephone instrument 20′connected to the TE device will only use a relatively small portion ofthe current potentially available at the TE device input terminals 18′.The difference between the current, and thus power, available at TEinput signal 70, and the actual power consumed by telephone instrument20′, is thus available to one or more power supplies such as powersource 75. With the one or more local power supplies such as powersource 75 being implemented with modern high efficiency SMPS designs,this additional power permits a new range of capabilities and featuresto be provided at a location normally considered limited to theavailability of a simple telephone instrument without providing any newwiring or AC mains to the location.

Further, the expected functions of traditional ringing and off-hooksignaling have been effectively preserved such that the SWC, or whateverprovides that function, would not be materially affected by provisioningof these new capabilities.

Further, one skilled in the art may appreciate that the additionalsignaling capabilities afforded by the out-of-band signaling channelsmay permit either additional types of signals to be exchanged betweenthe HE and TE locations, or more secure communication of sensitivesignals previously exchanged as DTMF or other forms of in-bandsignaling, or both. One example of signals that may benefit from thisadditional security are credit card or personal account access codes.

As described in connection with FIG. 2, the carrier frequency orfrequencies that are used to convey signaling information between the HEand TE portions of embodiment of the present invention are also relatedto the frequency discriminate filters identified as HPF's 43, 81 in FIG.2. Alternatively, it is possible to use one or more carrier frequenciesthat fit below the normal telephony voice frequencies for example in therange of 5 Hz to 120 Hz as the carrier frequency or frequencies insteadof, or in addition to, the higher frequencies previously described. Inthe case of such low frequencies carriers filters 43 and 81 would beconfigured as Band Pass Filters instead of High Pass Filters for thosecarriers. Because such low frequencies might be heard by the personsusing the overall system for voice communications it may be necessary toinclude a Band Reject or Notch Filter along with the BPF 34 and LPF 78functionality to reduce or eliminate objectionable artifacts related tosuch low frequency carriers. If both low and high frequency carriers areused within the same system each frequency range requires its ownfrequency discriminate filters of appropriate configuration.

A particularly useful choice for such a low frequency carrier is 60 Hzsince CODECs associated with SLIC functions typically already containband reject or notch filters to minimized anticipated 60 Hz hum coupledfrom AC mains carried on wires which may run parallel to telephonelines. This also applies to a carrier frequency of 120 Hz.

To appreciate the benefits of embodiments of the present invention it ishelpful to consider the practical power normally delivered to atelephone instrument with the power that may be delivered to the samelocation by use of embodiments of the present invention.

Assume for these first examples that the Voltage source is −48 VDC.

Further, in the traditional POTS case, assume that the ESR of the SLICis a fixed 480 Ohms. In a hypothetical case, please also assume that thetelephone instrument was unconstrained and was able to choose anyequivalent resistance for the sole purpose of maximizing the power itcould use. Further, let us assume that the telephone instrument waslocated at zero feet from the SWC SLIC terminals such that the totalline related resistance was 0 Ohms. In such a case, the telephoneinstrument would choose to match the source resistance of 480 Ohms andone-half of the source voltage would appear across the telephoneinstrument resulting in a loop current of 50 mA and 1.2 Watts beingdissipated by the telephone instrument and another 1.2 Watts beingdissipated in the ESR of the SLIC. Thus, the absolute maximum power thata traditional SLIC circuit can deliver to a traditional telephoneinstrument under these hypothetical ideal conditions is 1.2 Watts.

In another hypothetical case assume that the SLIC ESR was replaced by aconstant current source of ideal compliance and configured to deliver 22mA under all loop resistances and within the available source voltage.Again let us assume that the telephone instrument was located zero feetfrom the SWC SLIC terminals such that the line resistance was 0 Ohms. Insuch a case, the telephone instrument would choose to have a resistancewhich would place all of the available voltage across its own terminals.Since that voltage is 48 volts, the instrument would choose 2182 Ohmswhich would result in just less than 1.06 Watts being dissipated by thetelephone. Similarly, if the constant current source was configured tosupply 30 mA the chosen resistance would be 1600 Ohms and the powerdissipated would be 1.44 Watts.

The real world will neither have zero length lines nor telephones thathave only a requirement to maximize power dissipated. Real telephonelines are typically 24 AWG copper which exhibits a resistance of about50 Ohms per thousand feet for a twisted pair.

Assume now again the traditional −48 VDC source and 480 Ohm ESR and thatthe line length were 1000 Ft but the telephone instrument was still freeto ideally choose its ESR to maximize the power it dissipates. Thisresults in a 530 Ohm phone with just less than 1.09 Watts beingdissipated. At 4000 Ft the result would be a 680 Ohm phone with justunder 850 milliwatts dissipation.

With a constant current source of 22 mA from the =48 VDC source and 1000Ft of 24 AWG UTP, the phone would chose to have 2132 Ohms resistancewith maximum power would be 1.03 Watts while at 4000 Ft the phone wouldchose 1982 Ohms resistance with a dissipation of less than 960milliwatts. Similarly, for a 30 mA source, the 1000 Ft power would beless than 1.4 Watts and at 4000 Ft about 1.26 Watts with respectivephone resistances of 1550 and 1400 Ohms.

It is instructive to compare an embodiment of the present invention tosee what may be provided to the telephone instrument location from thesame −48 VDC level and then estimate the power available for otherpurposes beyond that required by the telephone instrument itself.

Assuming that the ESR of the Head End of the embodiment is about 60 Ohmsand then repeat the above calculations related to that configuration. Ifthe line length were zero, and there were no current limiting at all,then the telephone instrument along with any additional circuitrydesiring to use the excess power would choose an equivalent totalresistance of 60 Ohms which would result in 9.6 Watts being available atthe telephone instrument location. As the telephone itself requires onlyabout 100 milliwatts to operate, almost 9.5 Watts would be available forthe additional circuitry. But in the embodiment if we choose to describethe source current limiting fuses as being limited, in one example, at100 mA, then the phone would choose to have 420 Ohms resistance and themaximum power available would be about 4.2 Watts leaving 4.1 Wattsavailable for the additional circuitry.

One skilled in the art would appreciate the value of embodiments of thepresent invention even when the maximum current is limited to 100 mA andthe additional advantage of choosing a somewhat higher maximum currentlimit. Likewise, if the source voltage was selected to be a voltagehigher than 48 Volts, one can appreciate the yet higher power availablefor use by additional circuitry for otherwise identical line lengths orsimilar power over greater line lengths. Without listing all details asabove, in embodiments, the present invention would provide the followingapproximate total power capability at various source voltages andtelephone line lengths while retaining a 100 mA current limit. At 75 VDCTalk Battery: 6.4 Watts at 1000 Ft, 4.8 Watts at 4000 Ft, and 3.8 Wattsat 6000 Ft. At 100 VDC Talk Battery: 8.9 Watts at 1000 Ft, 7.4 Watts at4000 Ft, and 6.4 Watts at 6000 Ft. At 120 VDC Talk Battery: 10.9 Wattsat 1000 Ft, 9.4 Watts at 4000 Ft, and 8.3 Watts at 6000 Ft. Consideringthe same voltages and telephone line lengths but limiting the loopcurrent to less than 550 mA, and in most cases less than 400 mA is theactual current expected, then at 75 Volts the total power capabilitydeliver to the Tail End would be 12.7, 5.3, and 3.8 Watts respectively.From 100 VDC one would expect to have 22.5, 9.5, and 6.8 Watts availablerespectively. Finally, from 120 VDC one would expect to have up to 32.4,13.6, and 9.8 Watts available respectively. In all the above cases, thepower is made available under ELV/SELV conditions.

It will be apparent to one skilled in the art that embodiments of thepresent invention satisfy the needs and objectives outlined in thebackground and enables considerable flexibility for novelfunctionalities at heretofore unpowered physical locations that have atleast a single pair of telephone communications cable available.

V. EXAMPLE

The componentry described with respect to FIG. 2 was embodied in “frontend” and “back end” circuit boards shown in more detail in FIGS. 3 and 4respectively. FIG. 3 and FIG. 4 merely illustrate one implementation ofan embodiment of the present invention.

Referring first to FIG. 3, an example implementation of the HE portionof an embodiment of the invention. One skilled in the art willappreciate that in many cases several HE circuit blocks may beconveniently configured into a single assembly such that several TElocations might be served from a single HE location. While that was thecase for the physical HE devices assembled, it is also convenient toconsider a HE description as if it were a stand alone device as we shalldo here.

Power source 36′ is provided both for the “Talk Battery” (“TB”) and forthe bias requirements of the signaling and control electronics. In theexample construction, the TB selected was a traditional −48VDC obtainedfrom a custom power supply. A suitable commercially available isolatedAC input, DC output power supply is a VPS-25-48 available from CUI Incof Tualatin, Oreg. Likewise, the bias voltage in the exampleconstruction was obtained from the custom power supply. A suitablecommercially available isolated DC-DC power supply is aVWRBS1-D48-S5-SIP available from CUI Inc of Tualatin, Oreg. In thiscase, the TB supply also powers the bias supply. It is convenient toconnect the outputs of these separate DC power supplies such that theoverall result provides an SELV configuration along with a static drainresistor to earth ground. Referring now to FIG. 3, this arrangement isindicated by the AC line input cable 44 providing mains power to theisolated output 48 VDC power supply, a portion of 45. The traditionalpolarity for the TB is obtained by designating the more positive outputterminal of the 48 VDC supply as “common” signal 66 while the morenegative terminal provides TB signal 46. Rather than connecting the“common” terminal directly to earth ground as is normal practice in SWCsand similar equipment, the implementation provides a static charge bleedresistor 68 so that the resulting TIP and RING voltages may cover theInternational Electrotechnical Commission (“IEC”) Extra Low Voltage(“ELV”) range and retain a Safety Extra Low

Voltage (“SELV”) rating as contact with either TIP or RING terminal orelectrically conductive point does not have a direct path through earthground back to source 45. A suitable value for resistor 68 would be inthe range of 100K Ohms to 1 Meg Ohm. A suitable surface mount device(“SMD”) for this resistor is Vishay CRCW1206510KJNEA. As previouslymentioned, the bias power supply, a portion of power supply 45, mayconveniently be powered by the TB voltage source so that if a physicalbattery would be connected from 46 to 66, and a suitable isolatedbattery charger were to be used in place of the suggested precisionvoltage source described above, then all operating functions remainactive in the event of an AC power loss. It is convenient to connect themore negative output terminal of the bias supply to “common” signal 66and the more positive output terminal of the bias supply to “Vcc” signal67.

Item 38′, Low Pass Filter, serves to permit the passing of DC voltageand current from signal 46, 66 onto signal 35′. More specifically, thisLPF serves to protect the AC electrical signals existing on signal 35′from the shunting effect of the low capacitive reactance of capacitor 47and that of the Talk Battery power source portion of 45. Thus LPF 38′provides significant reactance at voice and signaling frequencies whileproviding a low ESR in series from signal 46, 66 to signal 35′. In theimplementation this is accomplished by the use of a split inductor wherehalf of the windings are in series with each the physical electricalconductors making up signals 46, 66 and 35′. These winding areconnected, or phased, such that the two inductances act in concert likea single total inductance with capacitor 47 appearing across theapparent center of the inductors halves. An advantage of this splitinductance arrangement is that while there is no true low resistance“ground” reference point as there would be in a traditional SWC,inductor 48 and capacitor 47 in concert provide excellent voice and highfrequency isolation between multiple channels of a multi-HEconfiguration. A suitable SMD capacitor for 47 is 220 μF, 100V partnumber EMVY101GDA221MMH0S available from United Chemi-Con of Rosemont,Ill. A suitable inductor would have significant inductance and low DCresistance for each winding As a suitable inductor was not commerciallyavailable, a custom inductor was designed and constructed on a smallphysical sized core and bobbin. The inductance of each winding was about2.5 H with a DC resistance of less than 12 Ohms. A suitable inductorwould be part number 11-5415A available from Tranex of Colorado Springs,Colo.

Items 39′, Protection Circuit, must take into account the low ESR natureof the main power source of the implementation. The primary function ofthis protection circuit is to limit current into or out of eitherterminal of the output conductor pair to a value that will protect theabove main power source should the output conductors be shortedtogether, to ground, or to some unintended external power source. Forthe purposes of the example implementation, the short circuit currentlimit was selected to be about 100 mA. Appropriate devices for thispurpose are resettable fuses 49 and 50 so that service may beautomatically restored following an event causing the fuses to open inorder to protect the system. Suitable resettable fuses for this purposeare Raychem (TYCO) part number TS250-130-RA available from TYCOIndustries of Menlo Park, Calif. If the TB supply of power source 36′implementation includes the current foldback characteristic previouslymentioned, then fuse elements 49, 50 are not required for short circuitprotection purposes.

Contact from an inadvertent source to either TIP or RING must beaccommodated safely and the most likely such source may have a voltageas high as 200 V peak such as from a 110 VAC hot lead. Due to the groundisolation provided by the implementation, such a voltage has only onereturn path back to its own ground reference that being through resistor68. With the example 510K Ohms and −48 VDC TB values, the maximumcurrent due to a 110 VAC hot lead touching the TIP lead somewhere wouldbe less than 400 microamps or less than 500 microamps if touching theRING lead.

As any fuse, including those utilized in this example, requires a finiteamount of time to react to an over-current condition additionalprotection may be warranted to protect the system from the effects ofvery brief events such as from voltages induced by nearby lightningstrikes. If an implementation is concerned about the possibility of suchinduced voltages, then additional protection in the form ofautomatically resettable overvoltage clamp 53 is prudent. These devicestypically present no effects upon the circuit until a high voltageappears on one or both of the output conductors. The devices thenquickly transition to a low resistance state shunting the abnormalvoltage to an appropriate reference point. As these devices typicallyand intentionally have quite low on-state forward voltages some smallresistance 51, 52 in series with each terminal will tend to limit theinrush current. These resistors should be closely matched so as tominimize longitudinal balance errors and should be able to dissipate thesmall but finite amount of power they would likely experience during afault condition. An appropriate value for these resistors is 10 Ohms,1%, and 0.5 Watt rated. Suitable SMD resistors for this purpose are Dale(Vishay) part number CRCW201010R0FKEF available from VishayIntertechnology of Malvern, Pa. If the induced voltage persists longenough the combination of voltage clamp 53 and series resistors 51, 52may give the resettable fuses 49, 50 time to open as well. A suitableactive voltage clamp is Littlefuse part number P1101CA2L available fromLittelfuse of Des Plaines, Ill.

Item 21′, Connector, is most often an industry standard telephonyconnector. A single Tip and Ring pair would thus typically use an RJ-11style jack while a 24 channel (24 Tip and Ring pairs) would thustypically use a 25 pair ribbon connector. A suitable SMD device for asingle channel connector is Molex part number 085513-5014 available fromMolex Corporation of Lisle, Ill. A suitable insulation displacementdevice for 24 channels is AMP (TYCO) part number 554090-1 available fromTYCO Industries of Menlo Park, Calif.

Item 23′, 28′, Relay, should meet typical telephony relay requirementsand use as little operating power as practicable. This relay is mostcommonly a DPDT (2 Form C) type with a low power magnetically biasedcoil. The coil voltage rating should be compatible with the electricaldrive available from the controller, Item 27′. If the controller isconfigured to operate from a 5 VDC bias voltage, then a suitable relayis NAIS (Panasonic) part number TXS2SA-4.5V available from AvnetElectronics of Phoenix, Ariz.

Item 24′, Ring Detector, may be a circuit commonly comprised of anoptocoupler of the ‘AC’ input variety in combination with a capacitor tocouple the ringing voltage to the optocoupler input LEDs while blockingany DC current through the optocoupler LED and a resistor in parallelwith the optocoupler LEDs such that in combination with the reactance ofthe capacitor at the ringing frequency ensures that a real ringingvoltage is present before the transistor output of the optocoupler isactivated. A suitable optocoupler is NEC part number PC2915-1-F3 whichexhibits a nominal LED forward voltage drop of 1.1 V and is availablefrom California Eastern Laboratories of Santa Clara, Calif. Anappropriate value for the shunting resistor is 10K Ohms and may be a SMD1/16 W due to the voltage limiting action of the optocoupler LEDs. Asuitable SMD resistor is Yageo part number RC0805J-0710KL available fromYageo USA of San Jose, Calif. To ensure ringing voltage detection downto 60 Vrms the capacitor should be at least 270 nF and 250 V. A suitableSMD capacitor is Panasonic part number ECW-U2274KCV available fromDigikey of Thief River Falls, Minn. A suitable output transistor pull upresistor may have a value of 10K Ohms. A suitable SMD resistor is Yageopart number RC0805J-0710KL available from Yageo USA of San Jose, Calif.

Items 27′, Signal Transceiver and Controller, is a circuit comprised ofa programmable microcontroller containing digital logic and analogdevice elements in addition to a programmable controller, random accessmemory for short term memory uses and programmable flash memory forprogram, configuration and operational settings. STC 27′ is providedwith resistors 62-65 to bias input signals for analog functions withinthe working limits of the microcontroller device. An appropriatemicrocontroller is Cypress Semiconductor part number CY8C27443-24PVXIavailable from Cypress Semiconductor of San Jose, Calif. Configurationand programming tools are provided by Cypress Semiconductor for thisseries of microcontrollers. Appropriate SMD resistors are Yageo partnumber RC0805J-0710KL available from Digikey of Thief River Falls, Minn.

Item 31′, Coupler, provides several functions including DC terminationof the SWC loop current, DC voltage isolation between the SWC providedvoltage and loop current, and bi-directional voice frequency coupling ofaudio signal energy between the SWC and the internal system side of thecoupler element. The coupling element would ideally cause no insertionloss into this last function. However, in many applications the smallinsertion loss due to the use of a quality transformer is justifiable ascompared to the cost and complexity of a lossless bi-directionalcoupling mechanism such as a transformer, or transformers, along withamplifiers and likely hybrid circuitry used to compensate for theinherent transformer losses while preventing self oscillation. If theSWC function is actually provided by an IAD or channel bank arrangement,it is likely possible to adjust these units to externally compensate forthe small inherent insertion loss of a single transformer design. Theexample implementation implements the coupler element based upon asingle transformer design where in the transformer 54 is implemented asa 600:600 Ohm split primary and split secondary design. Thistransformer, as implemented in the present example, must operatesatisfactorily while sustaining the net DC bias current of the SWC loopcurrent termination. A suitable transformer was not found to begenerally available from commercial sources. Thus custom transformerswere constructed to meet these criteria. A suitable transformer would bepart number 17-7183 available from Tranex of Colorado Springs, Colo. Thecenter terminals of each side of this transformer are bypassed for voicefrequency coupling purposes by 2.2 μF, 100 Volt, film capacitors. Itshould be noted that the voice frequency coupling (DC blocking)capacitor 56 on the secondary side of the transformer works in concertwith the components of item 34′ to provide the band pass nature of item41′. Suitable SMD capacitors for this purpose are Arcotronics partnumber LDEEF4220JB0N00 available from Kemet Corporation of Simpsonville,S.C. The side of the transformer associated with DC termination of theSWC loop, referred to as the primary side of the transformer, alsorequires a resistor or resistors in parallel with the afore mentionedcapacitor to provide DC termination of the SWC current loop when relay23′ is in the off hook state. The SWC termination impedance “Z” 55 maybe implemented by a complex impedance. In many cases however, especiallywhen the effective length of 15″ is relatively short, simple DCresistance to terminate the current loop of the SWC and a parallelcapacitance to minimize loss of AC coupling through the transformer isfunctionally effective. This resistance must be low enough to guaranteeoff hook detection by the SWC at maximum loop 15″ length while beinghigh enough to limit the current in the primary of the couplingtransformer according to the DC current limitation of the transformerdesign when loop 15″ electrical length is short. The present examplechose to use six 100 Ohm, 0.25 Watt SMD resistors in series for a totalof 600 Ohms, 1.5 Watts. Suitable SMD resistors are Yageo part numberRC1206FR-07100RL available from Yageo USA of San Jose, Calif.

Item 34′, Band Pass Filter, serves to pass voice frequenciesbi-directionally between signals 22′ and 35′ via coupler 31′ when relaycontacts 23′ are in an off-hook state while simultaneously blocking DCcurrent from passing through the secondary of transformer 54 of coupler31′. The DC blocking, or high pass component of this band pass filter isconveniently provided by the 2.2 μF capacitor 56 within coupler 31′circuit previously described.

BPF 34′ frequency characteristics are implemented in the present exampleby a pair of small inductors 58, 59 placed in series with the electricalconductors comprising the signals 33′ and 35′ in FIG. 3, along with anappropriate corresponding capacitor 57 across the electrical conductorsof signal 33′ in FIG. 2. For the prototype circuits it was determinedthat the most advantageous values of these components are 18 mH forinductors 58, 59 and 68 nF, 100V, 5% film for capacitor 57. Suitableinductors are Coilcraft part number RFB0810-183L available fromCoilcraft of Cary, Ill. A suitable SMD capacitor is Panasonic partnumber ECW-U1683JC9 available from Digikey of Thief River Falls, Minn.

Item 43′, High Pass Filter, serves to effectively pass the highfrequency carrier frequencies bi-directionally between signals 42′ and35′ of FIG. 3 while blocking DC voltages and any potential interferencefrom voice frequencies appearing on signal 35′.

HPF 43′ is implemented in the present example by a pair of smallcapacitors 60, 61 connected in series with the electrical conductorscomprising the signals 69, which is substantially similar to signal 35′,and 42 in FIG. 3. For the prototype circuit it was found that the mostadvantageous value is 330 nF, 100V, 10% film for capacitors 60, 61.Suitable SMD capacitors are Panasonic part number ECW-U1C334KC9available from Digikey of Thief River Falls, Minn.

Connector 16″ is most often an industry standard telephony connector. Asingle Tip and Ring pair would thus typically use an RJ-11 style jackwhile a 24 channel (24 Tip and Ring pairs) would thus typically use a 25pair ribbon connector. A suitable SMD device for a single channelconnector is Molex part number 085513-5014 available from MolexCorporation of Lisle, Ill. A suitable insulation displacement device for24 channels is AMP (TYCO) part number 554090-1 available from TYCOIndustries of Menlo Park, Calif.

Although connector 30′ may be defined by a specific application, inorder to provide for signals 41′, a common connector that may be easilyconfigured to a suitable size is a right angle header such as AMP4-103801-0 available from TYCO Industries of Menlo Park, Calif.

Referring now to FIG. 4, an example implementation of the TE portion ofan embodiment of the invention. One skilled in the art will appreciatethat in many cases a single TE circuit block may be associated with asingle telephone instrument 20″ location. However, it may also beconvenient to configure two or more TE circuit blocks within a singleassembly such as may be useful in a multi-user kiosk application.

Further, one skilled in the art may appreciate an arrangement where twoor more TE circuits blocks may connect via one or more IW telephone line17′″ pair to a single HE circuit block so long as the audio frequencychannels, which would effectively be in parallel, are either notutilized or that this parallel operation is beneficial, or at least notdetrimental, to the end application and that the signaling encoding issuch that the presumed, but optional, external devices connected totheir respective signaling connectors 90′ in FIG. 4 may beneficiallyutilize the common HE external signal 41 and connector 30 of FIG. 2.

Further one skilled in the art may appreciate that with an appropriateconfiguration of signals 89 and an appropriate one or more connector 90of FIG. 2 multiple external devices may conveniently share the power andsignaling capabilities afforded by the present implementation. Oneexample of such an implementation is the beneficial operation of two ormore biometric or other identification equipment associated with asingle telephone 20′ location. In embodiments, identification equipmentmay include a biometric device, a barcode scanner, a magnetic stripreader, a radio frequency identification tag reader, a camera, or amicrophone. Examples of biometric devices that may be implemented at thelocation of telephone equipment 20′ include but are not limited to afingerprint reader, an iris scanner, a retina scanner, and a palmscanner.

Connector 18″ is most often an industry standard telephony connector. Asingle Tip and Ring pair would thus typically use an RJ-11 style jack. Asuitable SMD device for a single channel connector is Molex part number085513-5014 available from Molex Corporation of Lisle, Ill.

Optional item 71′, Protection Circuit, must take into account the lowESR nature of the main power source of the implementation. The primaryfunction of this protection circuit is to limit current through theterminals of the input conductor pair 70′ to a value that will protectthe TE circuitry should some unintended external power source beconnected across terminals 18″ or the conductors of IW 17″′. Ifparticular implementation and installation conditions preclude such anevent, fuse elements 91, 92 may be omitted. For the purposes of theexample implementation, the current limit was selected to be about 100mA. Appropriate devices for this purpose are resettable fuses 91 and 92so that service may be automatically restored following an event causingthe fuses to open in order to protect the system. Suitable resettablefuses for this purpose are Raychem (TYCO) part number TS250-130-RAavailable from TYCO Industries of Menlo Park, Calif.

Contact from an inadvertent source to either TIP or RING conductors ofIW 17″ must be accommodated safely and the most likely such source maybe from a voltage as high as 200 V peak such as from a 110 VAC hot lead.Due to the ground isolation provided by the present implementation sucha voltage has no return path to earth associated with the TE.

As any fuse, including those utilized in this example, requires a finiteamount of time to react to an over-current condition, additionalprotection may be warranted to protect the system from the effects ofvery brief events such as from voltages induced by nearby lightningstrikes. If an implementation is concerned about the possibility of suchinduced voltages then optional additional protection in the form ofautomatically resettable overvoltage clamp 95 is prudent. These devicestypically present no effect upon the circuit until a high voltageappears across the input terminals 18″. The devices then quicklytransition to a low resistance state shunting the abnormal voltage to anappropriate reference point. As these devices typically andintentionally have quite low on-state forward voltages some smallresistance 93, 94 in series with each terminal will tend to limit theinrush current. These optional resistors should be closely matched so asto minimize longitudinal balance errors and should be able to dissipatethe small but finite amount of power they would likely experience duringa fault condition. An appropriate value for these resistors is 10 Ohms,1%, and 0.5 Watt rated. Suitable SMD resistors for this purpose are Dale(Vishay) part number CRCW201010R0FKEF available from VishayIntertechnology of Malvern, Pa. If the induced voltage persists longenough the combination of voltage clamp 95 and series resistors 93, 94may give the resettable fuses 91, 92 time to open as well. A suitableactive voltage clamp for this example circuit would have a standoffvoltage of 70 Volts ensuring a breakdown voltage no higher than 90Volts. A suitable SMD device for this purpose is Vishay part numberSMAJ70A available from Vishay Intertechnology of Malvern, Pa. If animplementation and installation is not concerned about inadvertentdifferential voltages appearing across IW 17″ conductors then items 93,94, 95, and perhaps 91 and 92 may be omitted.

Items 73′, Low Pass Filter, similarly serves to permit the passing of DCvoltages and current from signal 72′ onto signal 74′. More specifically,this LPF serves to protect the AC electrical signals existing on signal72′ from the shunting effect of the low capacitive reactance of theinput circuitry of power sources 75′. Thus LPF 73′ provides significantreactance at voice and signaling frequencies while providing a low ESRin series from signal 72′ to signal 74′. In the implementation this isaccomplished by the use of a split inductor 96 where half of thewindings are in series with each the physical electrical conductorsmaking up signals 72′ and 74′. These winding are connected, or phased,such that the two inductances act in concert like a single totalinductance with the input capacitor 97, along with any additional inputcapacitance of power sources 75′, appearing across the apparent centerof the inductors halves. A suitable inductor would have significantinductance and low DC resistance for each winding. As a suitableinductor was not commercially available, a custom inductor was designedand constructed on a small physical sized core and bobbin. Theinductance of each winding was about 2.5 H with a DC resistance of lessthan 12 Ohms. A suitable inductor would be part number 11-5415Aavailable from Tranex of Colorado Springs, Colo. A suitable SMDcapacitor for 97 is 220 μF, 100V part number EMVY101GDA221MMH0Savailable from Untied Chemi-Con of Rosemont, Ill.

LPF items 38′ of FIG. 3 and 73′ of FIG. 4 thus have basically the samecriteria of providing low resistance to DC signals while providingsignificant reactance to voice and signaling frequencies. For items 48of FIG. 3 and 96 of FIG. 4, an inductor with a resistance in the 10 to20 Ohm range and an inductance of around one half Henry per winding hasbeen found to be satisfactory for this purpose.

Local Power Source 75′ must operate from the available DC input voltageand provide a low voltage bias source, typically 5.0 VDC or 3.3 VDC, butmay be some other voltage or set of voltages as may be convenient, forthe electronic components and circuitry required to implement the activefunctions of the implementation. As such, this voltage/power convertermust be able to operate from the voltage provided by item 42 of FIG. 2which may be a nominal −48 VDC. One skilled in the art will recognizethat even if item 42 of FIG. 2 is a nominal −48 VDC, particularly if 42of FIG. 2 is implemented as a storage battery and battery charger, thissource voltage may vary over a range of perhaps 40 VDC to near 60 VDC.Due to the resistive losses inherent in Item 17″, the input voltage seenby Item 75′ may be substantially lower than even this, perhaps as low as10 to 20 VDC. Therefore, 75′ must be of as high an efficiency aspracticable and in the implementation is implemented as a Buck typeswitch mode power controller. Due to the potentially wide range of inputvoltages seen by this controller, the controller must be able to operateover this same input range of voltages, such as an example of 10 to 60VDC. It is further desirable for this controller to require a minimum of‘external to the controller’ components such as external switchingtransistors. A suitable controller for this purpose is NationalSemiconductor part number LM5574MT available from National Semiconductorof Santa Clara, Calif. A suitable inductor for use with this controllerin this application is a dual winding inductor connected such that onewinding is utilized as the buck inductor as described in NationalSemiconductor application notes for this controller while the secondwinding is configured to provide the operating bias voltage for thecontroller. A suitable SMD inductor for this purpose is Coiltronics(Cooper Bussmann) part number DRQ74-151-R available from Cooper Bussmannof St. Louis, Mo. One skilled in the art will appreciate that if two ormore separate voltages are required for such bias supplies, then eitherseparate, parallel input, SMPSs may be used, or generally it would bemore practical to set the SMPS to deliver the highest such voltage andthen use small linear regulators to drop this voltage to the remaininglower bias voltages.

Low Pass Filter 78′ serves to pass voice frequencies bi-directionallybetween signal 72′ and elements of 80′. In contrast with BPF 34′ in FIG.3, LPF 78′ must pass DC current as this current is required to power atelephone or similar function instrument 20″ if such an instrument isused by the application.

Items 34′ in FIG. 3 and 78′ in FIG. 4 otherwise have similar frequencycharacteristics and are implemented in the present example by the samecomponents as those described for BPF 34′ in FIG. 3. For reference,suitable inductors are Coilcraft part number RFB0810-183L available fromCoilcraft of Cary, Ill. A suitable SMD capacitor is Panasonic partnumber ECW-U1683JC9 available from Digikey of Thief River Falls, Minn.

Item 80′, Constant Current Limiter, Ring Generator, and Off-HookDetector, item 80 in FIG. 2, is shown in more detail being depicted asseparate functions Constant Current Limiter 103, Ring Generator 108, andOff-Hook Detector 109.

Constant Current Limiter 103 is provided in the implementation by theapplication of a voltage regulator of sufficient power dissipation andinput voltage capability configured as a constant current sourceincluding a small resistor to set the desired current, an appropriatecapacitor as required by the regulator for stability, and a larger audiofrequency bypass capacitor in parallel with the resulting circuit toprovide an electrically noise free current source. A suitable linearregulator for this purpose is National Semiconductor LM337T availablefrom National Semiconductor of Santa Clara, Calif. A resistor of 56.2Ohms, 1%, is used in the implementation to configure this regulator as a22 mA current source (no current will flow if item 20″ is not connectedand on hook). A suitable SMD resistor is Yageo part numberRC0805FR-0756R2L available from Yageo USA of San Jose, Calif. A suitableSMD capacitor for stability is Kemet part number T491A105M016ATavailable from Kemet Corporation of Simpsonville, S.C. A suitable SMDcapacitor for electrical noise suppression is Chemi-Con part numberEMVE101ADA330MJA0G available from United Chemi-Con of Rosemont, Ill. Ifthe source voltage made available from 36 of FIG. 2 is greater than 48volts, an LM337 could be forced to dissipate more power than that forwhich it is specified and this function would be replaced by, forexample, a SMPS regulator configured to provide the same resultingcurrent.

Item 84′, Option Ring Indicator, if needed by the intended application,may by implemented by the use of a pair complementary outputs of item77′ to drive a ceramic resonator at the resonators design frequency. Asuitable ceramic resonator is Kyocera part number KBS-20DB-2P-0,available from Kyocera International of San Diego, Calif., which isdesigned to operate at 2 KHz and up to 10 V peak to peak. In this case,the controller would provide both the driving pattern and voltage toproduce an appropriate audible signal.

Ring Generator 108, if needed by the intended application, may beimplemented by a custom circuit such as an appropriate circuit basedupon use of Unitrode part number UCC3752 available from TexasInstruments of Dallas, Texas or based upon use of Supertex part numberHV430 available from Supertex of Sunnyvale, Calif. It may be convenientto simply use an off the shelf ring generator module for this function.A suitable module is PowerDsine part number PCR-SIN06V48F00 availablefrom Microsemi of Irvine, Calif.

Off-Hook Detector 109 may be a circuit comprised of an optocoupler incombination with a resistor in parallel with the optocoupler LED suchthat the combination requires at least 5 mA, by standard practice,before the LED causes the optocoupler output transistor to activate. TheLED, with parallel resistor, is connected in series with one lead of thetelephone output connector observing the required polarity of the LED. Asuitable SMD optocoupler is NEC part number PC2913-1-F3 which exhibits anominal LED forward voltage drop of 1.1 V available from CaliforniaEastern Laboratories of Santa Clara, Calif. An appropriate value for theshunting resistor for use with this optocoupler is 160 Ohms and may be aSMD 1/8 W device due to the voltage limiting action of the optocouplerLEDs along with the 22 mA current limit provided in the implementation.A suitable SMD resistor is Yageo part number RC0805FR-0716ORL availablefrom Yageo USA of San Jose, Calif. A suitable output transistor pull upresistor may have a value of 10K Ohms. A suitable SMD resistor is Yageopart number RC0805J-0710KL available from Yageo USA of San Jose, Calif.If longitudinal balance is particularly critical in a particularapplication, then it may be advisable to use two optocouplers as above,along with each optocoupler LED shunt resistor, where one optocoupler isin series with each of the telephone output leads observing LED polarityrequirements. These optocoupler output transistors may be connected inparallel in this case and share a single pull up resistor and signalconnection to the associated controller 77′.

Connector 87′ may be an industry standard telephony connector. A singleTip and Ring pair would thus typically use an RJ-11 style jack. Asuitable SMD device for a single channel connector is Molex part number085513-5014 available from Molex Corporation of Lisle, Ill. However,particularly if the device used as instrument 20″ is something otherthan a standard telephone, some other type of connector may be moresuitable.

High Pass Filter 81′ is functionally the same as HPF 42′ in FIG. 3 andthus may utilize the same components. For reference, suitable SMDcapacitors are Panasonic part number ECW-U1C334KC9 available fromDigikey of Thief River Falls, Minn.

STC 77′ is functionally similar to and uses the same or amicrocontroller similar to that suggested for STC 27′ in FIG. 3. STC 77′is provided with resistors 112-115 to bias input signals for analogfunctions within the working limits of the microcontroller device. Forreference, an appropriate microcontroller is Cypress Semiconductor partnumber CY8C27443-24PVXI available from Cypress Semiconductor of SanJose, Calif. Configuration and programming tools are provided by CypressSemiconductor for this series of microcontrollers. Appropriate SMDresistors are Yageo part number RC0805J-0710KL available from Digikey ofThief River Falls, Minn.

Item 90′, Connector, would typically be application dependent so as toprovide a physical connector most convenient for the intendedinstallation or user. As the implementation anticipates that theauxiliary output voltage to be within SELV limits, and even commonly tobe less than 15 VDC at the power connector, if separate from anyauxiliary signal termination, may be of the common pin and sleeve type.A suitable connector is CUI part number PJ-102A available from CUI Incof Tualatin, Oregon. However, if the external device also utilizes theadditional signaling capabilities, then a more suitable connector wouldlikely accommodate both the auxiliary output voltage and unidirectionalor bidirectional signal or signals 89′ in a single physical device. Acommon connector that may be easily configured to a size suitable for aspecific implementation is a right angle header such as AMP 4-103801-0available from TYCO Industries of Menlo Park, Calif.

One skilled in the art will appreciate that the preceding example,including several component specifications, was intended to utilize a TBvoltage of −48 VDC as described. If, however, the additional benefitsafforded by a design utilizing a higher TB voltage, for example, up tothe 120 VDC ELV limit, then appropriate component and sub-circuitratings would have to be selected to be compatible with the highervoltage chosen.

Referring now to FIG. 5, an example implementation of the primaryfirmware functions of the HE portion of an embodiment of the invention.It is convenient to assume that the auxiliary or external devicesignaling functions are likely to occur either more frequently, at agreater rate, or should be more responsive to update requests than, forexample, the needs relating to basic telephony functions such as ringingor on or off hook transitions. Thus FIG. 5 depicts a simplified overallflow diagram that gives priority to the exchange of external device(auxiliary) signals between connectors 30 and 90 of FIG. 2.

Head End flowchart FIG. 5 depicts the execution logic of a Head Enddevice embodiment. The start point for the logic is the Begin symbol 200that is the logical equivalent of the End symbol 211, the designation ofthe endless logic loop

Item 200 is the entry point for implementation of the firmware functionsof the HE portion of an embodiment of the invention. The overall processdescribed below may be executed within STC 27′ of FIG. 3. The upperportion of FIG. 5 depicts an embodiment of a mechanism to addresschanges occurring at the HE and to encode and forward those changes to aTE embodiment. Likewise, the lower portion of FIG. 5 depicts anembodiment of a mechanism to address encoded signals received from a TEembodiment and to decode those signals to specific signals related toitems within or connected to the HE embodiment.

As indicated in the figure, a first decision point 201 determines if anyinput signals of signal 30′ of FIG. 3 associated with an external, thatis an auxiliary, device have changed during the interval since the priorexecution of the process herein described. If a change has occurred asdetermined by 201, then process step 202 is executed wherein the changedetected, or the resulting new state, is encoded by STC 27′ of FIG. 3onto the one or more carrier signals, and functionally transmitted ontoIW 17″ of FIG. 3 towards STC 77′ of FIG. 4. When process 202 is completecontrol passes to decision 203. If decision 201 determines that no inputsignals of signal 30′ have changed then control passes directly todecision 203 without executing process 202.

If decision 203 determines that the state of Ringing Detector signal 26′of FIG. 3 has changed then process 204 is executed wherein the changedetected, or the resulting new state, is encoded by STC 27′ of FIG. 3onto the one or more carrier signals, and functionally transmitted ontoIW 17″ of FIG. 3 towards STC 77′ of FIG. 4. When process 204 is completecontrol passes to decision 205. If decision 203 determines that signalof signal 26′ has not changed then control passes directly to decision205 without executing process 204.

Decision 205 determines if new encoded signals have arrived from IW 17″of FIG. 3. If decision 205 determines that no new encoded signals areavailable to decode then control passes to 211, and the entire processembodiment of FIG. 5 is complete. If decision 205 determines that somenew encoded signals are available to decode then control passes to 206.

Decision 206 determines if the new encoded signals include newinformation or new states directed towards an external or auxiliarydevice connected to connector 30′ of FIG. 3. If decision 206 determinesthat no new signals are directed towards an external or auxiliary devicethen control passes to 208. If new encoded signals directed towards anexternal or auxiliary device are determined to be available then process207 will decode the new signal or signals onto output signal portions ofsignal 30′ of FIG. 3. When process 207 is complete control passes todecision 208.

Decision 208 determines if the new encoded signals include a request toactivate or deactivate relay 23′ of FIG. 3 in the HE embodiment. Ifdecision 208 determines that a request to deactivate relay 23′ of FIG. 3has been received, then process 209 will cause signal 29′ of FIG. 3 tode-energize relay coil 28′ of FIG. 3 to effectively disconnect coupler31′ of FIG. 3 from the SWC signals on signal 15″ of FIG. 3. When process209 is complete control passes to decision 211, and the entire processembodiment of FIG. 5 is complete. If decision 208 determines that arequest to activate relay 23′ of FIG. 3 has been received then process210 will cause signal 29′ of FIG. 3 to energize relay coil 28′ of FIG. 3to effectively connect coupler 31′ of FIG. 3 to the SWC signals onsignal 15″ of FIG. 3. When process 210 is complete control passes todecision 310 and the entire process embodiment of FIG. 5 is complete.

Referring now to FIG. 6, an example implementation of firmware functionsof the TE portion of an embodiment of the invention. With assumptionssimilar to those mentioned above, FIG. 6 depicts a simplified overallflow diagram that gives priority to the exchange of external device(auxiliary) signals between connectors 30 and 90 of FIG. 2.

Head End flowchart FIG. 6 depicts the execution logic of a Tail Enddevice embodiment. The start point for the logic is the Begin symbol 200that is the logical equivalent of the End symbol 211, the designation ofan endless logic loop.

Item 300 is the entry point for implementation of the firmware functionsof the TE portion of an embodiment of the invention. The overall processdescribed below may be executed within STC 77′ of FIG. 4. The upperportion of FIG. 6 depicts an embodiment of a mechanism to addresschanges occurring at the TE and to encode and forward those changes to aHE embodiment. Likewise, the lower portion of FIG. 6 depicts anembodiment of a mechanism to address encoded signals received from a HEembodiment and to decode those signals to specific signals related toitems within or connected to the TE embodiment.

As indicated in the figure, a first decision point 301 determines if anyinput signals of signal 89′ of FIG. 4 associated with an external, thatis an auxiliary, device have changed during the interval since the priorexecution of the process herein described. If a change has occurred asdetermined by 301, then process step 302 is executed wherein the changedetected, or the resulting new state, is encoded by STC 77′ of FIG. 4onto the one or more carrier signals, and functionally transmitted ontoIW 17″′ of FIG. 4 towards STC 27′ of FIG. 3. When process 302 iscomplete control passes to decision 303. If decision 301 determines thatno input signals of signal 89′ have changed then control passes directlyto decision 303 without executing process 302.

If decision 303 determines that the state of Off-Hook Detector signal88′ of FIG. 4 has changed, then process 304 is executed wherein thechange detected, or the resulting new state, is encoded by STC 77′ ofFIG. 4 onto the one or more carrier signals and functionally transmittedonto IW 17″′ of FIG. 4 towards STC 27′ of FIG. 3. When process 304 iscomplete control passes to decision 305. If decision 303 determines thatno input signals of signal 88′ have changed, then control passesdirectly to decision 305.

Decision 305 determines if new encoded signals have arrived from IW 17′″of FIG. 4. If decision 305 determines that no new encoded signals areavailable to decode then control passes to 310, and the entire processembodiment of FIG. 6 is complete. If decision 305 determines that somenew encoded signals are available to decode, then control passes to 306.

Decision 306 determines if the new encoded signals include newinformation or new states directed towards an external or auxiliarydevice connected to connector 90′ of FIG. 4. If decision 306 determinesthat no new signals are directed towards an external or auxiliary devicethen control passes to 308. If new encoded signals directed towards anexternal or auxiliary device are determined to be available then process307 will decode the new signal or signals onto output signal portions ofsignal 89′ of FIG. 4. When process 307 is complete control passes todecision 308.

Decision 308 determines if the new encoded signals include a request toactivate or deactivate alerting equipment that may be included in the TEembodiment. If decision 308 determines that no new alerting functionchange signals are included in the new signals then control passes to310. If decision 308 determines that new alerting function changesignals are included in the new signals then process 309 will enable,disable, or cycle the alerting, or ringing embodiments that may beincluded in the TE embodiment via signal 83′ and/or signal 85′ of FIG.4. When process 309 is complete control passes to decision 310, and theentire process embodiment of FIG. 6 is complete.

The foregoing description has been provided with particular reference todeployment of the invention in an incarceration institution. However,the invention may have numerous other advantages. For example, it can bedeployed to reduce or eliminate “wall-warts” associated with peripheraltelephone devices in a home. It can be used to enable peripheral devicesefficiently in other environments where rewiring would not be aseconomical. For example, it can be used to enable camera capability at aremote existing telephone used for screening access to a physicalfacility, e.g., a commercial manufacturing facility or office structure,the main gate of a ranch, compound or other real estate of significantsize or even with an intercom used at the door of a residence. Theinvention may be useful in many other applications.

1-26. (canceled)
 27. An apparatus for providing direct current through atwo-conductor cable connecting a remote power source to a localcommunications device having one or more additional capabilities,features and devices that require power in excess of that delivered by atraditional telephone network line, the apparatus comprising: a low passfilter configured to receive a direct current power signal from theremote power source to produce a filtered direct current power signal,the low pass filter being remote from the local communications device,having a low equivalent series resistance, and having a significantreactance at voice and signaling frequencies thereby mitigating non-DCsignal attenuation when the filtered direct current power signal iscombined with higher frequency alternating current signals that assistin the operation and control of the local communications device havingone or more additional capabilities, features and devices; and one ormore protection systems configured to mitigate damage to the powersource in the event of a short or other fault condition and having a lowequivalent series resistance.
 28. The apparatus of claim 27, wherein theone or more protection systems are selected from: (i) one or moreresettable fuses having a low equivalent series resistance and (ii) acurrent foldback circuit.
 29. The apparatus of claim 28 wherein the lowpass filter comprises a split inductor.
 30. The apparatus of claim 29,wherein windings of the split inductor are in series with each of twoelectrical conductors carrying the direct current.
 31. The apparatus ofclaim 29, wherein the one or more protection systems comprises one ormore resettable fuses having a low equivalent series resistance.
 32. Theapparatus of claim 29, wherein the one or more protection systemscomprises a current foldback circuit.
 33. The apparatus of claim 29,wherein the one or more protection systems further comprises at leastone resettable overvoltage clamp.
 34. The apparatus of claim 29, furthercomprising a bus to combine the filtered direct current power signalfrom the low pass filter with one or more higher frequency alternatingcurrent signals that assist in the operation and control of the localcommunications device having one or more additional capabilities,features and devices.
 35. The apparatus of claim 29, further comprisinga bus to combine the filtered direct current power signal from the lowpass filter with a higher frequency alternating current signal thatenables at least one of: (i) the transmission of data to the localcommunications device having one or more additional capabilities,features and devices, and (ii) the transmission of data from the localcommunications device having one or more additional capabilities,features and devices.
 36. The apparatus of claim 29, further comprisinga bus to combine the filtered direct current power signal from the lowpass filter with a higher frequency alternating current signal in thevoice frequency range that enables the transmission of voice signals toand from the local communications device having one or more additionalcapabilities, features and devices.
 37. The apparatus of claim 29,wherein the local communications device having one or more additionalcapabilities, features and devices is employed in an institutionalenvironment and includes a camera communication device for remotevisitation and one or more of internet and intranet access for accessingan account and conducting transactions.
 38. The apparatus of claim 29,wherein the local communications device having one or more additionalcapabilities, features and devices includes one or more of: (i) abiometric reader, (ii) a barcode reader, or (iii) an RFID reader,configured to identify or verify the identity of an individual bydetection of information embedded within one or more of: (i) awristband, (ii) a fingerprint, (iii) a palm print, (iv) voice print orspeaker recognition, (v) retinal or iris scan, or (vi) otheridiosyncratic personal characteristic.
 39. The apparatus of claim 29,wherein the local communications device having one or more additionalcapabilities, features and devices includes one or more of: (i) a stillphotograph camera, (ii) a video camera, (iii) an internet connectivitydevice, (iv) an intranet connectivity device, (iv) an analog voicetransmission device, and (v) a digital voice transmission device. 40.The apparatus of claim 29, wherein the direct current power signal fromthe remote power source is supplied at about 48 volts or less and about25 milliamps or less.
 41. The apparatus of claim 29, wherein the directcurrent power signal from the remote power source is conducted issupplied at more than 48 volts up to about 120 volts.
 42. The apparatusof claim 29, wherein the direct current power signal from the remotepower source is supplied at more than 25 milliamps up to about 550milliamps.
 43. The apparatus of claim 29, wherein the direct currentpower signal from the remote power source is supplied at more than 25milliamps up to about 400 milliamps.
 44. The apparatus of claim 29,wherein the direct current power signal from the remote power source issupplied at a voltage determined by a current needed at the localcommunications device and a length of the two-conductor cable.
 45. Theapparatus of claim 29, wherein the low pass filter has an equivalentseries resistance less than that of BORSCHT functions.
 46. An apparatusfor providing direct current through a two-conductor cable connecting aremote power source to a local communications device having one or moreadditional capabilities, features and devices that require power inexcess of that delivered by a traditional telephone network line andproviding at least one high frequency signal for operation and controlof the local communications device having one or more additionalcapabilities, features and devices, the apparatus comprising: a firstlow pass filter configured to receive a direct current power signal fromthe remote power source to produce a filtered direct current powersignal, the first low pass filter: (i) being remote from the localcommunications device, (ii) having a low equivalent series resistance,and (iii) having a significant reactance at voice and signalingfrequencies thereby reducing non-DC signal attenuation when the filtereddirect current power signal is combined with higher frequencyalternating current signals that assist in the operation and control ofthe local communications device having one or more additionalcapabilities, features and devices; a first high pass filter configuredto filter a high frequency alternating current signal to produce afiltered high frequency alternating current signal, the first high passfilter being employed to mitigate interference between the directcurrent power signal and the filtered high frequency alternating currentsignal when combined; a bus configured to combine the filtered directcurrent power signal and the filtered high frequency alternating currentsignal to produce a combined direct current power and high frequencysignal to assist in the operation and control of the localcommunications device having one or more additional capabilities,features and devices; one or more first protection systems configured tomitigate damage to the power source in the event of a short or otherfault condition and having a low equivalent series resistance; atwo-conductor cable configured to transmit the combined direct currentpower and high frequency signal to one or more second protection systemsassociated with the local communications device having one or moreadditional capabilities, features and devices; a second protectionsystem configured to mitigate damage in the event of a short or otherfault condition; a second low pass filter configured to receive at leasta portion of the combined direct current power and high frequency signalfrom the second protection system to produce a local premises directcurrent power signal; a second high pass filter configured to receive atleast a portion of the combined direct current power and high frequencysignal from the protection system to produce at least one local premiseshigh frequency signal; and one or more connectors configured to transmitthe local premises direct current power signal and the local premiseshigh frequency signal to the local communications device having one ormore additional capabilities, features or devices to assist in theiroperation and control.
 47. The apparatus of claim 46, wherein the one ormore first protection systems are selected from: (i) one or moreresettable fuses having a low equivalent series resistance and (ii) acurrent foldback circuit.
 48. The apparatus of claim 47, wherein thefirst low pass filter comprises a split inductor.
 49. The apparatus ofclaim 48, wherein the second low pass filter comprises a split inductor.50. The apparatus of claim 48, wherein the first low pass filtercomprises a split inductor wherein windings of the split inductor are inseries with each of two electrical conductors carrying the directcurrent.
 51. The apparatus of claim 48, wherein the first protectionsystems comprises at least one resettable fuse having a low equivalentseries resistance.
 52. The apparatus of claim 48, wherein the firstprotection systems comprises a current foldback circuit.
 53. Theapparatus of claim 48, wherein the one or more second protection systemscomprises at least one resettable fuse having a low equivalent seriesresistance.
 54. The apparatus of claim 48, wherein the bus is configuredto combine the filtered direct current power signal from the first lowpass filter with a filtered high frequency alternating current signaloutside a voice frequency range.